A US woman who shot and killed her husband and two adult children before taking her own life is thought to have committed the shocking crime as a result of being ostracised from the religion she was raised in.

Every time I tell a mate I’m doing a story on cryptocurrency, they invariably ask me the same two questions: should they invest their own hard-earned money, and which cryptocurrency will get them a Lamborghini/yacht/island quickest?

"We must call on our MPs, particularly those in the Senate to reject these abhorrent attacks on Medicare in the form of co-payments."

The protest shut down the CBD for around 30 minutes as protesters peacefully marched to Sydney Town Hall before returning to Hyde Park for a free concert by popular indie band The Jezebels.

Meanwhile in Melbourne, human rights advocate and lawyer Julian Burnside told around 10,000 protesters they can expect to see Tony Abbott in the dock in an international court.

"The way they are treating refugees in Australia is a crime, and there has already been a reference put into the international criminal court complaining of that very treatment," Mr Burnside said.

"If you feel exhausted keeping up the pressure on the government, if you feel so tired you can't keep going, just support yourselves with the vision of Tony Abbott and Scott Morrison in the dock at The Hague."

The crowd also jeered as a large Tony Abbott puppet waved at them with smoke coming from its rear, representing a person with their pants on fire.

In Brisbane, organisers blamed complacency for a relatively poor turnout.

The Queensland government's anti-bikie laws and plans to sell assets were among the issues discussed, as well as the plight of refugees and the Great Barrier Reef.

Organisers claim 5000 people took part in Sunday's rally but police say no more than 1200 participated in the Brisbane CBD protest.